Apparatus for classifying minerals and other substances by flotation



Jan. 26, 1960 H. SCHRANZ APPARATUS FOR CLASSIFYING MINERALS AND OTHER SUBSTANCES BY FLOTATION 4 Sheets-Sheet 1 Filed Aug. 13, 1958 I w E.

HUBERT LUDWIG SCHRAN Z INVENTOR ATTORN EY Jan. 26, 1960 H. SCHRANZ APPARATUS FOR CLASSIFYING MINERALS AND OTHER SUBSTANCES BY FLOTATION 4 Sheets-Sheet 2 Filed Aug. 13, 1958 HUBERT LUDWIG SCHRANZ ATTORNEY Jan. 26, 1960 H. L. SCHRANZ 2,922,521 APPARATUS FOR CLASSIFYING MINERALS AND OTHER SUBSTANCES BY FLOTATION Filed Aug. 15, 1958 4 Sheets-Sheet s z- -6 7 E. W L 5 HUBERT LUDWIG SCHRANZ INVENTOR MW QM ATTORN EY Jan. 26, 1960 H. L. SCHRANZ APPARATUS FOR CLASSIFYING MINERALS AND OTHER SUBSTANCES BY FLOTATION 4 Sheets-Sheet 4 Filed Aug. 13, 1958 HUBERT LUDWIG SCHRANZ INVENTOR wm ATTORN EY United States Patent APPARATUS FOR CLASSIFYING MINERALS AND OTHER SUBSTANCES BY FLOTATION Hubert Ludwig Schranz, Clausthal-Zellerfeld, Germany Application August 13, 1958, Serial No. 754,765

Claims. (Cl. 209-163) This invention relates to an apparatus for classifying minerals and other substances by flotation.

A flotation apparatus for coal is known, in which a pulp to be floated is fed by a centrifugal pump together with air and the floating reagents to an agitation cell, which is constructed substantially as a cylinder or prism, the discharge pipe of the pump opening laterally. into the cell approximately at half the height of the latter.- The pulp is withdrawn from the bottom of the agitation cell and is partly recycled to it for re-flotation. The air bubbles with the coal particles adhering thereto should rise above the discharge opening of the pressure pipe in the cell and should collect on the surface of the pulp to form a froth. It is a disadvantage that the pulp entering the cell flows downwardly, opposite to the rising air bubbles. This movement of the pulp and of the air bubbles in opposite directions prevents a clear separation between the tailings (dirt) and pure coal. The flow in opposite directions causes also a strong mechanical stress to be applied to the solids-laden air bubbles rising from the lower part of the cell whereby the solids are at least partly torn from the bubbles so that the time of flotation must be prolonged. Another disadvantage re-,

sides in the fact that the pulp is introduced laterally, i.e., unsymmetrically, into the cell. With this kind of introduction a uniform distribution of the air bubbles throughout the cross-section of the cell cannot be achieved. On the other hand, the success of a flotation of minerals, particularly with respect to a particularly short flotation time, depends not only on the correct selection of the flotation reagents but to a high degree also on a really uniform distribution of the air bubbles in the pulp.

It is an object of the invention to avoid the above disadvantages in a simple manner. The invention is based on a flotation apparatus having a cylindrical or prismatic agitation cell and a pump whereby the pulp to be floated is fed to the agitation cell together with air and, if desired, also with flotation reagents, whereas part of the pulp emerging from the agitation cell is recycled to the cell for re-flotation.

The solution of this object resides in that the height of the pulp column in the agitation cell is about 1.5 to 3.5 times the width of the cell, that a funnel with froth discharge means is provided at the top of the agitation cell, that the funnel has an overflow for discharging part of the pulp flowing thereto from the agitation cell and is provided at the bottom with a pipe connected to the suction side of the pump and serving for recycling the pulp to be re-flotated, that the discharge pipe of the pump opens centrally or approximately centrally into the cell from below and that the pulp-air mixture emerging from the discharge pipe rises in the agitation cell as a jet to a height which is about 0.5 to 0.75 times the height of the pulp column. Up to that level the pulp-air mixture flows as a more or less coherent stream. This means that the velocity of the mixture emerging from the discharge pipe has been slowed down at this point to such an extent 2,922,521 Patented Jan. 26, 1960 I that the contents of the cell above said level is not sub jected to any considerable or disturbing turbulence but is moved upwardly at an approximately uniform velocity. The latter is due to the fact that the rising jet spreads uniformly throughout the cross-section of the cell in the form of a mushroom as its velocity decreases. In this way the air bubbles contained in the jet are also uniformly distributed throughout the cross-section of the cell. The air bubbles rise then without obstruction in the zone of still pulp above the jet. Because the jet carries the solid particles entrained by it mainly vertically upwardly, in the same direction in which the air bubbles are rising too, the adherence of the solid particles to the air bubbles is greatly facilitated and at the same time a shaking or shearing of the solid particles from the bubbles is substantially prevented. For this reason the apparatus according to the invention enables a reliable flotation even of unusually coarse particles, e.g., coal having a grain size up to 2 mm., with high efficiency.

An advantageous development of the apparatus according to the invention resides in that the agitation cell is shaped in adaptation to the upright jet as an inverted pyramid or cone having a point angle of about 20-50".

The very uniform distribution of the air bubbles, on the one hand, and the fact that the direction of flow of the pulp in the agitation cell is substantially in agreement with the direction in which the air bubbles rise, on the other hand, permit of a high pulp throughout per minute. The pump is advantageously dimensioned for a capacity per minute amounting to about twice to ten times the capacity of the flotation cell.

Two illustrative embodiments of the invention are shown in the drawing, in which:

Fig. l is a side view showing a flotation plant comprising two flotation units,

Fig. 2 is an appertaining top plan view,

Fig. 3 is a sectional view taken on line III-III of Fig. 2. I

Fig. 4 is a cross-sectional view taken on line IV-IV in Fig. 3, and

Fig. 5 shows an agitation cell of simpler construction.

The plant shown in Figs. 1 to 4 consists of two flotation units I and II. Each of these flotation units has an agitation cell '1, which is constructed as a Slender inverted pyramid and has an acute angle of about 25. The discharge pipe 2 of a centrifugal pump 3 or 3' extends vertically upwardly and is connected to the bottom point of the cell. The discharge pipe is provided with a short pipe 29, which extends into the agitation cell. The agitation cell is provided with an inclined bottom 30 slightly spaced below the outlet opening of this pipe.

The agitation cell has connected to its lowermost point a pipe 31 or 31', which incorporates desirably an adjustable and shut-ofl valve 32. The suction pipe 4 of the pump has a pipe 5 connected thereto, which incorporates a throttle flap 6. Air under pressure is introduced or sucked from the atmosphere by the pump through the pipe 5. In the latter case the pipe is upwardly prolonged sufficiently to extend above the pulp level in the agitation cell. In this way an escape of pulp through said pipe during an inoperative period is prevented. A pipe 7 for supplying the pulp to be floated is connected to the suction pipe of the pump 3.

The agitation cell is provided at its top with a funnel 16 of rectangular cross section, which is provided at its bottom with a discharge pipe 18 or 18'. The inside wall of the funnel is connected to' the agitation cell by means of a curved surface 17. The top edge of this surface is desirably provided with an overflow weir 19, which is adjustable in height by means not shown. The funnel 16 and the agitation cell are surrounded at the top by vertical walls 8, 9, 10 and 11, which together form a froth box. The wall 11 is somewhat lower than the other walls and is provided at its top edge with a chute 12, which serves for discharging the froth and terminates over a discharge trough 13. The wall 11 is preferably provided on the inside with a weir 26, which is also vertically adjustable. The top edge of the weir is provided with a downwardly inclined plate 14, over which a rotary paddle wheel 15 is arranged.

It is apparent from Fig. 1 that an opening 33' is provided in the right-hand wall of the funnel 16. 'As is apparent from Fig. 3, this opening has the form of a narrow rectangle in cross-section and is preferably arranged as remotely as possible from the wall11. Outside the funnel the opening 33 leads to a box 3.4, which is divided bya vertical wall 35 into two compartments 36, 37. The wall terminates at its upper edge substantially on the same level as the upper edge of the curved surface 17 and'is preferably provided at this point with a vertically adjustable weir 38. A pipe 39 or 3.9 is connected to the bottom of the compartment 37.

As is seen from Fig. 1 the two flotation units 1 and. II are connected in series, the pipe 39' leading to the suction pipe of the centrifugal pump 3'. It is also apparent from Fig. 1 that the pipe 18 discharges into the pipe 7 and the pipe 18' discharges into the pipe 39. The same figure shows that the pipe 31 is also connected to. the.

pipe 39.

In operation the centrifugal pump 3 sucks the pulp, e.g., a coal pulp which is to be flotated and to which the fl'otating reagents have previously been added, from theconduit 7. At the same time, air under pressure is introduced through the pipe 5 at a rate which. can be controlled by the throttle flap 6. The pulp passing through the pump is thoroughly mixed with the reagents and the air. It is obvious that a centrifugal pump, is particularly suitable to ensure a thorough mixing of the pulp with. the air and the reagents. In order to minimize the wear of the pump, it is suitable to use a pump theimpeller and guide device of which are covered with wear-resistant material, such as rubber. Besides, a centrifugal pump discharges the mixture practically without swirl, which is of great advantage for the purposes of the invention.

Another suitable pump, e.g., a jet pump, may be usedinstead of a centrifugal pump. Where another pump is used and even with a centrifugal pump it is suitable to provide in thedischarge pipe a guide member, e.g., a.

directional spider 21, to eliminate any swirl.

The mixture is driven by the pump as an upwardly directed jet 22 into the agitation cell, which is filled with pulp. The pulp column in the cell has a height H measured from the outlet'of the pipe 29. The pump is selected, particularly regarding its speed, to cause the jet to rise to a level A-A, the height h of which is about- 0.5-0.75 times the height H. As is apparent from the drawing the jet expands in the cell like a mushroom and finally extends throughout the cross-section of the cell. The air bubbles entrained by the. jet are evenlydistributed throughout the cross-section as the jet expands. They rise then vertically upwardly through the zone a of stilled pulp. Thus, the solids entrained by the jet are moved substantially in the same direction in which the air bubbles rise. This facilitates the adherence of the coal particles to the air bubbles. Besideathe fact that the jet is practically free of swirl and of changes in direction ensures that the solid particles adhere to the bubbles and are notshaken or sheared off. For this reason the flotation apparatus according to the invention has a high throughput and a high yield. The pump is desirably selected for a capacity per minute which is about 2-10 times the capacity of the flotationcell.

The front with the adhering coal particles collects on the pulp level in a bed 25 and isdriven from there by meansof the paddle wheel 15 over the plate 14, the weir 26 and the chute 12 into the trough 13.

h p lp fl ws across e ir .int t e funnel: 16,

from which part of the pulp flows through the pipe 18 into the pipe 7, where it mixes with the fresh pulp flowing through this pipe and is returned therewith through the pump 3 and the pipe 29 into the agitation cell. In this way, part of the pulp is continuously recycled, which is very favorable.

The other part of the pulp is discharged from the funnel 16 through the opening 33 and rises then in the compartment 36 and flows across the weir 38 into the compartment 37. The weir 38 is adjusted so that its top edge is substantially level with the top edge of the weir 19.

Thus, the weir forms an overflow, across which only such an amount of pulp can flow from the funnel as fresh pulp is being supplied to the agitation cell through the pipe 7.

The substantial spacing of the opening 33 from the wall 11 ensures that the froth is discharged across this wall without disturbance by the discharged pulp. The discharged pulp flows from the compartment 37 through the pipe 39 into the flotation unit II, where it is reflotated. The pulp passing therefrom into the pipe 39' is discharged from the plant. Additional flotation units connected in series as has been described hereinbefore may be connected to the pipe 39' to enable any desired number of re-fiotations.

Any coarse grain separated in the agitation cell of the flotation unit I settles on the inclined bottom 30. The valve 32 incorporated in the pipe 31 enables part of the pulp to be withdrawn continuously or when required from the lower part of the agitation cell. This part of the pulp will entrain the settled coarse grains and passes them through the pipe 31 to the pipe 39, whence it enters the flotation unit II for re-flotation. Any coarse grain settled therein is periodically or continuously discharged together with pulp through the pipe 31' or is fed to a subsequently arranged flotation unit. This eliminates the danger of a clogging of the agitation cells in the course of time by settled coarse particles. Moreover, the inciined' bottoms with the pipes connected thereto facilitate the removal of any settled solids from the agitation cells after. a prolonged inoperative period.

In flotation plants having a particularly simple construction the agitation cells may take the form of an elongated vessel as is shown in Fig. 5. The cell 40 shown here has an upper portion in the shape of a square section prism and a lower portion in the form of a pyramid 41. The discharge pipe 42 of a centrifugal pump 43 is centrally connected to the lower point of the pyramid. This pipe is continued by a short pipe 44, which extends into the agitating cell. An inclined bottom 45 provided below the outlet end of this pipe and a pipe 46 is connected to the agitation cell at the lowermost point of this bottom. The column of the pulp in the cell has a height H measured from the outlet end of the pipe 44. This height is about 1.5 to 3.5 times the width B of the cell. The pulp-air mixture discharged by the pipe 44 is driven upwardly in the cell as a jet 47 to a height 11 which is about 0.5 to 0.75 times the height H As has been described hereinbefore the jet expands like a mushroom in the cell. The above-mentioned ratio between H and'B ensures that the jet expands uniformly throughout the cross-section of the cell so that the entrained air bubbles are uniformly distributed throughout the, cross-section. of the cell.

The prismatic cell may be replaced by a cylindrical one. In this case the height of the pulp column in the agitation cell is about 1.5 to 3.5 times its diameter.

Whereas the flotation of coal has been mentioned hereinbefore as an example the invention may also be applied to the flotation of any other substances which are suitable for flotation.

Ashas been stated hereinbefore the agitation vessel must be very slender to ensure that its upper portion is filled w th air b b les. s unif rmly possible.

I claim:

1. A flotation apparatus which comprises an agitation cell having a bottom inlet and an overflow and adapted to hold between said inlet and overflow a column of pulp the height of which is about 1.5 to about 3.5 times the largest width of said cell, a funnel disposed at the top of said cell and arranged to receive pulp from said overflow, said funnel being provided with froth discharge means and with an overflow arranged to withdraw a part of the pulp received from said overflow of said cell, a pump having a discharge pipe substantially centrally connected from below to said cell and a suction pipe adapted to receive fresh pulp to be flotated, and a pipe connecting the lower end of said funnel to said suction pipe, said pump being operable to adrnix air to said pulp received by said suction pipe and to feed the resulting mixture of pulp and air through said discharge pipe into said cell to cause said mixture to form in said cell a jet rising to a height which is about 0.5 to 0.75 times the height of said column.

2. A flotation apparatus as set forth in claim 1, in which said cell is cylindrical at least in its upper portion.

3. A flotation apparatus as set forth in claim 1, in which said cell is prismatic at least in its upper portion.

4. A flotation apparatus as set forth in claim 1, in which said cell consists at least in its lower portion of a downwardly tapering body having a point angle of about 20.

5. A flotation apparatus as set forth in claim 1, which comprise a pipe connected to said discharge pipe and having an open top disposed in said cell and in which said agitation cell has an inclined bottom under said open top,

and which comprises a pipe connected to the lowermost point of said bottom and adapted to Withdraw settled coarse particles.

6. Apparatus as set forth in claim 1, in which said discharge pipe contains swirl suppressing means.

7. Apparatus as set forth in claim 6, in which said swirl suppressing means consist of guide means.

8. Apparatus as set forth in claim 1, in which said pump is dimensioned to have a capacity per minute which is about 2 to 10 times the capacity of the agitation cell.

9. A flotation process which comprises providing a pulp column having a height which is about 1.5 to about 3.5 times the largest width of said column, withdrawing pulp from the top of said column, removing froth from the froth layer above the said Withdrawn pulp mixing part of said withdrawn pulp from which said froth has been removed with fresh pulp and with air to form a mixture of pulp and air, and introducing said mixture into said column in the form of a jet rising from the lower end of said column to a height which is about 0.5 to about 0.75 times the height of said column.

10. A flotation process as set forth in claim 9, in which the volume of said mixture introduced into said column per minute is about twice to ten times the volume of said column.

864,856 Norris Sept. 3, 1907 McLean July 28, 1942 

